Since before Ben Franklin's historic kite-flying experiment in 1752, humans have been unlocking and unraveling the many mysteries surrounding electricity. Today, nearly every gadget and piece of machinery uses electricity to operate, spanning from the very small (e.g., nano-robots) to the very large (e.g., industrial drives and other high-power machinery). The present application relates to the latter. In particular, this application relates generally to medium- and high-voltage motors, such as three-phase AC (alternating current) motors.
Today's power plants generate three-phase AC electricity, and that electricity is stepped down and/or rectified to provide the specific level and type of power needed for a given application. In the case of driving larger motors, this may be done using inverter cells. For example, FIG. 1 depicts an example configuration for driving a three-phase AC motor. As shown in the figure, three-phase electricity may be supplied by the local power company to an input side of a transformer 101. The output side of the transformer 101 may include secondary windings 102a-f, each of which may provide three-phase AC input to three power cells 103a-c. In some situations, the same pair of secondary windings (e.g., 102a-b) may supply inputs to all three cells 103. The transformer 101 serves to-isolate the power cells 103 from the power source, and may also be used to step up or down the voltage level and/or adjust the phase output.
The power cells 103a-c receive the two sets of three-phase power inputs, and each provides two output terminals (e.g., Uo and Vo). One of these terminals (Vo) is tied to the corresponding terminal in the other cells, while the other terminal (Uo) provides an output from the cell to a phase input on a three-phase load, such as motor 104. These outputs of the three cells 103 may be identical in amplitude, and may be offset from one another by 120 degrees of phase.
The highest power level supportable by the FIG. 1 configuration depends on the circuit components used in the power cells 103, and their various voltage ratings. Higher rated components will support higher voltage levels, but such components are more expensive, and the output voltage required by some applications can even exceed the highest-rated components. Accordingly, there is a need for higher power level configurations that can perhaps minimize the cost by not requiring these higher power level cells.